Possible involvement of alpha 2-adrenoceptor on the hypnotic action of flunitrazepam

Diazepam augments gender differences in cutaneous LD flux response to local cooling

Cutaneous vasoconstriction in response to local cooling is normally greater in females than in males. Cold induces amplification of alpha2-adrenoceptor affinity for norepinephrine and increases reflex sympathetic thermoregulatory output. Benzodiazepines are drugs with very well-known binding to the central and peripheral benzodiazepine receptors. Besides these effects they decrease sympathetic output and as it was shown in the last decade they act synergistically with alpha-adrenoceptors. In the present study we tested the hypothesis that the benzodiazepine diazepam interacts with an alpha-adrenoceptor mechanism at the level of microcirculation. We measured laser-Doppler blood flux changes provoked by local cooling before and after oral application of a low dose of diazepam (5 mg) in 9 healthy males and in 11 healthy females with regular menstrual cycles. The results of our experiments show that in females there is a significant reduction (ANOVA, p < 0.05) in laser-Doppler flux during the first four minutes of cooling after taking of diazepam. In males, there is no significant difference in the responses to cold before and after an application of diazepam. Our results suggest that diazepam, in addition to its well-known effect on BZ receptors may also interact with alpha2C-adrenoceptors in the vessel wall during local cooling.

Alpha-2 adrenoceptor activity affects propofol-induced sleep time

alpha(2) Adrenoceptor activity is involved in the mechanism of anesthesia. Clonidine, a alpha(2) adrenoceptor agonist, and yohimbine, a alpha(2) adrenoceptor antagonist, increase and decrease barbiturate-induced sleep times. In this study, we examined the effects of these drugs on propofol-induced sleep time. One-hundred-eighteen male Wistar rats weighing 320-400 g were used. Rats received saline, yohimbine (1, 0.1, or 0 mg/kg), or clonidine (300, 30, 3, or 0 microg/kg) intraperitoneally followed by 60 mg/kg of propofol in various combinations. In two series of experiments, either sleep time or prefrontal cortex norepinephrine release (microdialysis) was measured. One milligram/kilogram of yohimbine decreased propofol-induced sleep time to approximately 70% of control, and this was accompanied by an increase in perfusate norepinephrine of approximately 240% of control. Clonidine increased sleep time approximately 260% (300 microg/kg) and approximately 170% (30 microg/kg), and this was accompanied by a decrease (approximately 60% in both doses) in perfusate norepinephrine. In the present study, we show that the alpha(2) antagonist, yohimbine, decreased and the alpha(2) agonist, clonidine, increased propofol-induced sleep times. These changes were essentially mirrored in both groups by changes in norepinephrine release in the prefrontal cortex.

IMPLICATIONS

Central alpha(2) adrenoceptor is thought to be involved in several IV anesthetics-induced sleep. In this study, activation of the receptor increased the propofol-induced sleep time, whereas its inhibition decreased the sleep time. The results provide further evidence that the alpha(2) receptor is a good tool to elucidate the mechanism of anesthetics-induced sleep.